Re: [PATCH 3/3] mm/memcg: Unify swap and memsw page counters

[Waiman Long]

On 8/20/20 11:46 AM, Shakeel Butt wrote:
> On Thu, Aug 20, 2020 at 6:04 AM Waiman Long <longman@xxxxxxxxxx> wrote:
> > The swap page counter is v2 only while memsw is v1 only. As v1 and v2
> > controllers cannot be active at the same time, there is no point to keep
> > both swap and memsw page counters in mem_cgroup. The previous patch has
> > made sure that memsw page counter is updated and accessed only when in
> > v1 code paths. So it is now safe to alias the v1 memsw page counter to v2
> > swap page counter. This saves 14 long's in the size of mem_cgroup. This
> > is a saving of 112 bytes for 64-bit archs.
> >
> > Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> > ---
> >   include/linux/memcontrol.h | 3 +--
> >   mm/memcontrol.c            | 8 +++++---
> >   2 files changed, 6 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index d0b036123c6a..d2a819d7db70 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -216,10 +216,9 @@ struct mem_cgroup {
> >
> >          /* Accounted resources */
> >          struct page_counter memory;
> > -       struct page_counter swap;
> > +       struct page_counter swap;       /* memsw (memory+swap) for v1 */
> >
> >          /* Legacy consumer-oriented counters */
> > -       struct page_counter memsw;
> >          struct page_counter kmem;
> >          struct page_counter tcpmem;
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index d219dca5239f..04c3794cdc98 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -68,6 +68,11 @@
> >
> >   #include <trace/events/vmscan.h>
> >
> > +/*
> > + * The v1 memsw page counter is aliased to the v2 swap page counter.
> > + */
> > +#define memsw  swap
> > +
> Personally I would prefer a union instead of #define.

Yes, that is also what I am thinking about in the v2.

Cheers,
Longman